The probe affects Ford Escape and Mercury Mariner SUVs and Ford Fusion and Mercury Milan sedans from the 2009 through 2011 model years.

The National Highway Traffic Safety Administration says the vehicles can unexpectedly go into "limp home mode" at reduced power. The agency and Ford have received almost 1,500 complaints about the problem. There were three crashes and one injury.

The agency began looking into the cars and SUVs after getting a request from the North Carolina Consumers Council last year. Nonprofit safety groups and consumers can petition the agency to investigate vehicle problems.

The cars and SUVs haven't been recalled, but the investigation could lead to a recall.